Tuesday, May 29, 2018

Glenoid version - measurement and importance in shoulder arthroplasty

These authors point out that the use of computed tomography (CT) to measure glenoid version adds cost and radiation exposure in comparison to standard radiographs.

They present a method for assessing glenoid component version after TSA using routine preoperative CT and postoperative radiographs.

They measured preoperative glenoid version using established methods with an axillary x-ray, 2-dimensional CT, and patented commercial Glenosys software.

They measured postoperative glenoid component version and inclination for 61 TSA patients using patented commercial Mimics software for preoperative CT and postoperative x-rays. Glenoid implantation and imaging were performed on 14 cadavers, allowing validation of results against the gold standard postoperative CT glenoid retroversion measurement.

Compared with the gold standard, retroversion and inclination measurement error was 2° ± 1°and 2° ± 1°, respectively. Average postoperative version correction was 6° ± 7°, with 35 of 61 patients (57%) corrected to <10° of retroversion. Correlation between preoperative version measurement methods was
good to very good, except on the axillary x-ray. Patients not corrected to <10° of retroversion had significantly higher preoperative retroversion (14° ± 6°) than those corrected to <10° (6° ± 7°; P < .00001).

Comment: As pointed out by the authors, it is important to minimize cost and radiation exposure by avoiding CT scans that do not affect the clinical outcome of the patient. It is also important to avoid expenditures on patented commercial software, again unless it can be shown to improve the clinical outcome of surgery.

In the assessment of glenoid version, we have found that a standardized plain axillary view provides the information necessary to plan and conduct shoulder arthroplasty without the need for CT scans. However, the view needs to be standardized as shown in the figure below (see this link)

While the authors express concern that "Glenoid component loosening after total shoulder arthroplasty (TSA) may occur if retroversion is not corrected to <10°", this concern was not validated in a recent publication "Does Postoperative Glenoid Retroversion Affect the 2-Year Clinical and Radiographic Outcomes for Total Shoulder Arthroplasty? which analyzed the clinical outcomes of 71 TSAs performed using a standard all-polyethylene pegged glenoid component inserted without effort to change glenoid version. This study compared the outcomes in the 21 in which the glenoid component was implanted in 15° or greater retroversion (mean ± SD, 20.7° ± 5.3°) with the 50 in which it was implanted in less than 15° retroversion (mean ± SD, 5.7° ± 6.9°). At the 2-year followup the mean (± SD) improvement in the SST (6.7 ± 3.6; from 2.6 ± 2.6 to 9.3 ± 2.9) for the retroverted group was not inferior to that for the nonretroverted group (5.8 ± 3.6; from 3.7 ± 2.5 to 9.4 ± 3.0). The mean difference in improvement between the two groups was 0.9 (95% CI, - 2.5 to 0.7; p = 0.412). The percent of maximal possible improvement (%MPI) for the retroverted glenoids (70% ± 31%) was not inferior to that for the nonretroverted glenoids (67% ± 44%). The mean difference between the two groups was 3% (95% CI, - 18% to 12%; p = 0.857). The 2-year SST scores for the retroverted (9.3 ± 2.9) and the nonretroverted glenoid groups (9.4 ± 3.0) were similar (mean difference, 0.2; 95% CI, - 1.1 to 1.4; p = 0.697). No patient in either group reported symptoms of subluxation or dislocation. With the numbers available, the radiographic results for the retroverted glenoid group were similar to those for the nonretroverted group with respect to central peg lucency (four of 21 [19%] versus six of 50 [12%]; p = 0.436; odds ratio, 1.7; 95% CI, 0.4-6.9), average Lazarus radiolucency scores (0.5 versus 0.7, Mann-Whitney U p value = 0.873; Wilcoxon rank sum test W = 512, p value = 0.836), and the mean percentage of posterior humeral head decentering (3.4% ± 5.5% versus 1.6% ± 6.0%; p = 0.223). With the numbers available, the percentage of patients with retroverted glenoids undergoing revision (0 of 21 [0%]) was not inferior to the percentage of those with nonretroverted glenoids (three of 50; [6%]; p = 0.251).

This suggests that it may be possible to effectively manage arthritic glenohumeral joints without specific attempts to modify glenoid version.

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